ENH: Add ROI fill-in functionality to 'searchlight' command
DOC: Speed up example and add to tests
ENH+CMD: Make explicit note about "broken" commands (fixes gh-181)

Move command import logic into bin/pymvpa2. Catch ImportErrors and mark
the related command as "not available" in the docs without causing an error.
Merge remote-tracking branch 'gh-master/cmdline_modular' into cmdline_modular

* gh-master/cmdline_modular:
  ENH: consistent (more TODO) use of assert_raises + check for Range to not be type dependent
  RF/ENH: constraints -- use __or__ and __and__ for concise semantics, improved testing, EnsureValue -> Constraint
  ENH: docstrings for constraints' __init__ and use semantic *constraints,*values instead of pure *args
  BF: executable perms for few cmdline examples missing them
  BF,DOC: add import of base.constraints to suite + minor typo